TYPES, COMPOSITION AND PROPERTIES OF SOIL
Subject:
Agricultural Science
Class:
SS 1
Term:
Second Term / 2nd Term
Week:
Week 6
Topic:
TYPES, COMPOSITION AND PROPERTIES OF SOIL
Previous Knowledge: The pupils have previous knowledge of
SOIL FORMATION AND PROFILE DEVELOPMENT
that was taught in their previous lesson.
Behavioural Objectives : At the end of the lesson, learners will be able to
- Say the meaning of Soil
- Mention types of Soil
- Say Soil Composition
- Highlight Physical Properties of Soil
- Define Soil Classification Systems
Instructional Materials
- Wall charts
- Online Resource
- Textbooks
- Laptop
- Soil samples
- Flash cards
- www.edudelighttutors.com
Methods of Teaching
- Role modelling
- Questions and Answers
- Explanation
- Discussion
- Recitation
- Imitation
- Story Telling
- Dramatization
Content:
Meaning of Soil
Soil is the loose weathered material covering the earth surface which supports the growth of plants and sustains human and animal life.
Soil consists of mineral materials e.g. sand, clay, silt and gravel, organic materials which are made of plants and animals, H2O (water), air and microbes.
Types of Soil
There are three types of soil formed as a result of the breakdown of rocks that is weathering. They are as follows:
1. Clay SoilThis is a type of soil that has clay constituting the major proportion about 40% and above while
the other part contains silt and sand. Types of crops that can grow on clay soil: rice, sugarcane,
etc. It possesses the following characteristics.
Properties or Characteristics of Clay Soil
The relative range in diameter is 0.002mm
It is fine grained
It is plastic in nature
It is sticky when wet
It has tiny pore spaces
It is poorly drained and aerated
It has high water retention capacity
It can easily form ribbons or cast when moulded
Capillarity is very high
When dry, it is hard and cracks thereby leading to deep crevices in the dry season.
It is alkaline and there is high proportion of mineral ions in the colloidal clay forms.
It supports water – logging and erosion
It is heavy, hence it is difficult to cultivate.
The colour is usually light brown
Percolation is low.
The particles are tightly bound together with little pore spaces.
It is usually fertile and good for agriculture
It has good chemical properties but bad physical properties.
It has electrical charges which help to attract large number of mineral ions.
Ways or Methods of Improving Clay Soil
Addition of organic manure
Addition of lime to reduce the acidity in the soilProper and adequate drainage Economic Importance of Clay Soil It is use for pottery and crafts making Building houses Construction works Rearing fish
2. Sandy Soil
These are loose soils which consist of coarse grain particles. It is a type of soil which sand particles are much more than the other soil particles (about 85%) and others 15%. Types of crops that can grow on sandy soil: cowpea, soyabean, groundnut, etc.
Characteristics or Properties of Sandy Soil The soil particles are large, coarse, grained and gritty when touched. It is well aerated with loose, large pores or air spaces. It possess low water holding capacity The water rise by capillary is very low. When wet it is not sticky and hence cannot be moulded into shapes It does not support water-logging and erosion Farmers can easily work on them i.e. it can be tilled Leaching is high Low plant nutrient Highly acidic It is usually white in colour High percolation Micro-organism are discharged because of heat
It has poor chemical properties by good physical properties.
It is neither suitable for growing tree crops nor for most food crops but it is used for pasture crops and vegetable. It is made up of quartz, that is S1O2 The range in diameter is between 2.00m and 0.02mm Methods of Improving Sandy Soil By mulching Planting cover crops Application of compost manure Application of farm yard manure Avoidance of bush burning Economic Importance of Sandy Soil
Sandy Soil: Is very important in building construction when mixed cement for block moulding, plastering and concreting. Varieties of crops such as cowpea, cotton groundnut, cassava, can be cultivated on it.
. Loamy Soil
This is a mixture of sand and clay particles with a higher proportion of organic matter (humus). It is a combination of both silt and clay without any one dominating the other. This makes the soil to have features of both silt and clay,the color vary from brown to black. It is also known as an artificial soil. Types of crops that can grow on loamy soil: best for all crops
Properties or Characteristics of Loamy Soil It is an all round soil It is rich in plant nutrients. It has the drainage of sand and loose particles. It can withstand moderate periods of drought It contains decayed organic matter or humus
It is alkaline in nature. It is well aerated Loams are easily worked or cultivated in both dry and wet forms The lumps fall apart easily and so they are friable. They are classified as heavy, light or medium according to the proportion of clay. Has high water-holding capacity. Percolation is low and capillarity is high It is dark in colour It has a good combination of silt, clay and sand fraction. It is the best soil for Agriculture.
Humus is not a soil but the decaying matter in the soil. It is usually black or dark brown in colour, moderately smooth when touched. It helps in binding the soil particles together. It is also helps in increasing the soil nutrients.
Soil Composition Chemical and Biological Composition of Soil
Plant foods are the nutrients or mineral elements that a plant requires for growth, maintenance and development. Soil minerals which is also referred to as inorganic matter constitute about 45% of the soil composition. Plants nutrients are divided into two groups:
Macro nutrients Micro nutrientsMacro Nutrients (Major/Essential)
These are the mineral salts required in large amount and their deficiency can easily manifest on plants. They include Nitrogen potassium, calcium, magnesium and sulphur. They are also known as major elements.
Micro Nutrients or Minor or Trace Elements
They are the mineral salts required in small quantity, and their deficiency does not easily manifest but can manifest on the animals feeding on such plants.
Micro nutrients are also known as trace elements or minor elements. They include carbon, iron, manganese, molybdenum, boron, zinc, cobalt, copper and chlorine.
Oxygen and hydrogen can also be grouped as minor elements. NB: Iron is a traced element in plants but of major elements in animals.
Soil Water
This constitutes about 25% of the soil. It is the amount of water present in the soil and available to plants.
Source of soil water are ground water rainfall and irrigation.
Types of Soil Water These are three types of soil water, namely:Gravitational: The excess water subtended by gravity on soil surface. This water is not available to plants. It is often pulled down beyond the reach of roots. It helps to prevent water logging in soil.
Capillary water: This is the form of water which rises above the water table in the soil. It can be held by surface tension in the pores. This water can rise to the root zone of plants especially in clay soils of the soil. The finer the pores, the greater the force binding the water and higher the rise of water. This form of water is easily available to plants.
Hygroscopic water: This is the form of water which is absorbed on the surface of soil particles from atmospheric water vapour. It is only available for plant for a short time before it vapourizes. It can easily get loss when the soil is oven dried at about 1050 This water is not available to the plants for their growth.
Terminologies Used in Soil Water
Field capacity: Type of water left in the soil after evaporation and drainage have occurred. The soil will be wet and water left is still available to plant for use.
Water table: Is the reservoir of water that is slightly below the reach of the largest tap root and above the parent materials. The higher the water table, the higher the amount of water available to plants.
Surface tension: Is a force which holds water molecules in the soil. The cohesion force holds water molecules together thereby preventing water from falling after rising while adhesion attaches water molecules to soil particles, and makes water to be available at a particular point in the soil.
Water log: This is when water is too much in a soil covering the whole soil surface. The excess water can be removed by drainage.
Wilting point: Is the point at which the soil has lost so much water or has been lacking water for a very long time that it cannot absorb water again when eventually supplied.
Importance of Soil Water to Crops Helps in the absorption of mineral salts Helps in the transportation of nutrients to other parts of the plants. It is needed as a raw material during photosynthesis.
For hydrolysis of food substances like starch, proteins, fats and oil which are later transported to other parts of the plants. It is a constituent of plant protoplasm Essential for plant growth
Helps in the coding of crops Helps to maintain plant turgor / turgidity Essential for enzymes to work very well in plants. It neutralizes the effect of temperature. Promotes the activities of micro-organisms.
Soil Living Organisms
This includes the living organism in the soil. The soil consists of both plants and animals. Some of them are beneficial while others are harmful.
Soil living organisms are divided into two groups:
Macro-organisms Micro-organism
Macro-organisms: They are higher organism living in the soil which is readily visible. Examples include Earthworms, worms, millipedes, cricket, centipedes, insects, snails and rodents.
Micro-organisms: They are small soil living organisms. Examples are bacteria, fungi, and algae
Effects/Importance of Soil Organisms Soil organisms are involved in the decomposition of dead organic matter in the soil. They include micro-organisms like bacteria, fungi and algae. They help in burrowing, which lead to good soil aeration and water movement. They help in influencing chemical changes in the carbon and nitrogen cycles. They help in improving the structure of the soil When the soil organisms die, they add nutrients to the soil. The decayed ordecaying bodies of
both plants and animals are also known as humus(5%).
Symbiotic bacteria like Rhizobium leguminosarium found in the root nodules of legumes like beans, groundnut, help in fixing atmospheric nitrogen to the soil. Some soil micro-organisms produce acidic materials which are essential in rock weathering.
Some soil organisms can be harmful or detrimental, causing diseases to animals, plants and man. Soil organisms are affected by erosion, burring and fertilizer application. They help in the process of weathering.
Soil Air
This is the amount of gases found inside the soil. It is essential for respiration of soil microorganisms. The amount of air is inversely proportional to the amount of water in the soil, that is; its amount depends on the size of the soil particles and the amount of soil water. It is about 25% by composition.
Importance of Soil Air Soil air provides a medium of gaseous exchange for soil living organisms. It is essential for the process of germination to take place in the soil. It prevents certain plant diseases caused by anaerobic organisms e.g. damping off. It provides a medium of transpiration for plant roots. It helps in absorption of plant nutrients. Essential for root development
Carbon dioxide and sulphur dioxide react with water to form weak acids which aid weathering of rocks.
Soil CompositionTypes, Composition and Properties of Soil – Soil composition
Soil pH
The (Pondus de Hydronum) is defined as the measure of hydrogen and hydroxyl ion concentration in the soil. They determine the acidity, alkalinity and neutrality of the soil. The hydrogen concentration is also known as the acidity of the soil while, hydroxyl ion concentration is also known as the alkalinity of the soil. This is a chemical factor
Determination of Soil pH This is the process of testing the pH of the soil.
The following methods are used:
Use of litmus papers The use of BDH universal indicator Field testing using printed colour standards Determination of soil pH colouring metrically The use of electrometric method pH Scale
This is a scale which is graduated from 0 to 14, and developed to measure both the hydrogen ion concentration (acidity) and hydroxyl ion concentration (alkalinity) of the soil.
pH scale pH scale analysis is as follows: pH2 = strongly acidicpH6 = slightly or weakly acidic
pH7 = neutral
pH8 = slightly alkaline or weakly alkaline
pH13 = strongly alkaline
pH 5.5 – pH 7.5 = best pH for plant and soil organisms
Causes of Soil Acidity
Application of fertilizers like Ammoniumtetraoxosulphatevi(CNH4)2 SO4), and Ammonium
trioxo-nitare v (NH4NO3)
Acid rain especially in petroleum exploring areas.
Presence of sulphur in the soil – sulphur undergoes oxidation and distribution to form weak
acid in the soil.
Through leaching of the soil.
Nutrient uptake by plants which are later harvested.
Presence of sulphur, which alone can reduce the pH to about 2 which makes the soil to be
highly acidic.
Control of Soil Acidity
Application of lime e.g. limestone, dolomite, gypsum, slaked lime, quick lime
Application of wood ash.
Application of manures like compost, green and farm yard manures.
Application of bone meal.
Importance of Liming
It neutralizes soil acidityIt improves soil structure It releases calcium ions to plants. It increases the rate of water percolation. It reduces the toxicity of dissolved copper and manganese in the soil. It increases the activities of soil micro-organisms.
Physical Properties of Soil (a) Soil Texture
This refers to the relative proportion of various sizes and groups of individual soil grains in a mass of soil. It is the degree of fineness or coarseness of soil as determined by the size and distribution of the primary particles. It may also mean the relative proportions of different sizes of mineral particles in the soil. Texture is an important physical characteristic of a soil. Water and air movement depends partly on the soil texture.
Methods of Determining Soil Texture Feeling Sieve method Sedimentation method By moulding Importance of Soil Texture It determines the degree of coarseness or fineness of a soil sample. It determines the type of crops to be cultivated or grown in a farm land.
It can reveal the different types of soil particles e.g sand, fine sand, coarse sand, silt and clay.
The proportion of the different fractions determines the type of soil. The size or fractions or texture of the various soil types are as follows: Fractions
Size (in mm)
Stone Greater than 200mm Gravel 200 – 20mm Fine gravel
20 – 0.2mm
Coarse sand 2 – 0.2mm Fine sand
0.2 – 0.02mm Silt 0.02 – 0.002mm
Clay Less than 0.002mm It enables the farmer to determine the level of erosion in the farmland. It determines the rate of percolation and leaching in the soil It helps to determine the tillage practice to be adopted by the farmer. It help the farmer to determine the level of irrigation/drainage to be carried out on the farm (b) Soil Structure
This is the arrangement of soil particles into various aggregate sizes and shapes. It may be also defined as the physical appearance of the soil according to the arrangement of the individual particles.
Importance of Soil Structure It helps to determine the porosity of the soil It helps to determine the rate of percolation The level of fertility is determined or absorption of water in the soil It also supports the growth of crops It determines the ease with plant roots can penetrate the soil It prevent water-logging.
Methods of Preserving Soil Structure Planting cover crops Mulching Application of manure Application of lime fertilizers Reducing activities of machines Types of Soil Structure Single grained structure Coherent structure. Crumb structure. Granular structure Prismatic structure Plate-like structure Block-like structure
Diagram Showing Types of Soil Structures Types, Composition and Properties of Soil – Types of Soil Structures
Soil Classification Systems
Soils are classified in different ways. The type of classification adopted depends on the physical characteristics of soil such as texture, its depth, fertility or even the amount of soluble salts present.
In Nigeria soils are classified into the following classes:
(i) Ferruginous Tropical Soils: These are soils with different horizons.They are found both in thesouthern and northern parts of Nigeria. The soils respond generally to where there is availability of phosphate and nitrogenous manure.
Examples of crops grown here are yam, maize, cassava, upland rice, oil palm, cocoa, (southern) while guinea corn, cotton, groundnut, millet, rice, sugar cane and tobacco are successively grown in the northern parts
(ii) Ferri Soils: These are generally considered as transitional soil. They have retarded profile development due to erosion. They have high organic matter contents. They are deficient in available phosphate. This soil is found in Ogoja and Benue. It supports the growth of oil palm and maize.
(iii) Ferratallitic Soils: These are acidic and infertile. They can be improved by sulphate of potash, super phosphate and sulphate of ammonia.
(iv) Eutrophic Brow Soil: This type of soil is well structured and found in the B-horizon. The fraction of clay is 2:1. It is developed on volcanic ash, is common in plateau and Adamawa areas of Northern Nigeria. It is considered as young soil when compared to other types. It supports crops like Banana, Oil palm, rubber, cocoyam, plantain and elephant grass.
(v) Calcimorphic Soil: It contains large quantities of relativity soluble compounds of calcium. It is rich in clay. It is badly erosion over a large area. It can be protected through adequate soil conservation.
(vi) Vertisols: This type of soil contains more than 30% clay. It has a cation exchange capacity in the excess of 30mg / 100g of soil. It is found in the northern part of Nigeria precisely Maiduguri and Gombe. Cottons and Sorghum are successively grown here.
Presentation :
The topic is presented step by step
Step 1: The class teacher revises the old topic
Step 2: The class teacher introduces the new topic
Step 3: The class teacher allows the pupils to give their own contributions and gives room for pupils” participation
Class Teacher and Pupils Activities. Interaction or Participation
This involves class teacher and pupils’ interaction, conversation, imitation or modeling through discussion, play method or just by recitation or asking and answering questions that are related to the topic that has just been taught.
EVALUATION QUESTIONS
1. List and explain the three types of soil
2. State 5 properties of each types of soil mentioned in (i) above
3. State five importance in each of the following soil compositions: (i) Soil water (ii) soil air (iii) soil pH.
4. State or list two physical properties of soil. (b) Mention five important factors of (i) soil texture (ii) soil structure. (c) State five ways or systems of classifying soil.
5.(a) Explain fully the terms; (i) soil texture (ii) soil structure (b) How do they influence crop production? (c) (i) What is soil pH? (ii) At what pH range is soil said to be acidic? (iii) State three adverse effects of soil acidity with regard to soil reaction and plant growth.
6. State five properties each of the following soils: (i) sandy soil (ii) clay soil (iii) loamy soil.
7. Comment on the pH status of a sample of soil which indicates the reading pointer at (i) 5.6-7.5 (ii) 2.0 (iii) 13.0 (iv) 8.0 (v) 6.0 (b) Mention three factors each responsible for soil acidity and alkalinity in the soil. (c) State two corrective measures of removing alkalinity in the soil (d) List five liming materials.
8. Write short notes on the following: (i) soil macro nutrients (ii) soil micro nutrients (iii) soil air (iv) soil water.
Conclusion :
The class teacher concludes the lesson by giving the pupils some notes on the topic that has just been taught. He goes round to mark and he does the necessary corrections.
